The present invention relates to an information transmission system in which an information storing and supplying apparatus supplies information to an information receiving apparatus via a network.
There have been many information transmission systems, in which users retrieve information stored in an information storing and supplying apparatus (hereinafter, referred to as "a server") using an information receiving apparatus (hereinafter, referred to as "a user terminal") via a network, for example, the Internet.
For information transmission services using the Internet, at first, a user accesses a server that stores data required by the user and requests that the server send main data (Home Page). By the access, the server identifies the user to send the main data. Upon receiving the main data from the server, if necessary, the user chooses detailed data in reference to a list in the main data and requests that the server supply the detailed data to the user. In response to the request, the server supplies the user with the requested detailed data. This allows data transmission services to be rendered over the Internet. Similarly, in information transmission systems in other networks for specific purposes or general purposes, other than the Internet, servers have supplied users with information in response to the users'requests.
In above conventional information transmission systems, the user can receive only information that has already been stored by the time of the accessing. Consequently, the user cannot capture any later updating of the received information.
For example, some information suppliers, or some servers, frequently update their information on on-the-spot broadcasted baseball games and on odds of horse races, if there are any changes. Accordingly, the conventional information systems burden users who require updated information, with necessary frequent accesses to their servers. However, the information is not always updated. As a result, their repetitive accesses sometimes lead to vain efforts. In view of the amount of traffic amount over the network, such useless accesses hinder an efficient information transmission system. In particular, for information transmission systems that accommodate many users'terminals, frequent accesses might cause congestion and so forth.
There has been another method of capturing updated information, which is employed in the text broadcasting system: servers continually supply up-to-date information over network while users intercept information that seems necessary to the users. Pursuant to the method, however, the users might take much information that is unnecessary to the users, which only permits the users to obtain little information that is necessary to the users. Because much information is supplied in spite of little information that is necessary to the users, the method proves not to be an efficient information transmission system.
Furthermore, information has always involved revision numbers and update time, which are available only as the revision numbers and update time are available themselves.
If a clock in a user's terminal is incorrect despite an exact update time, the terminal that intends to implement some processes based on the update time, might experience trouble as follows: assuming that the terminal is designed to discard any information, including update time, that seems to lie in the future in terms of its clock, the incorrect clock possibly causes the terminal to discard all information provided by servers.
Moreover, the amount of supplied information is often large. In this case, the information should be divided into many pieces. However, such pieces possibly reach the user in an order different from an original order, depending on network condition. With packet communication, the order of the received pieces is confirmed in reference to the sequence numbers of packets. If the order differs from the original order, the pieces may not reproduce the information, this is, the above confirmation does not compensate for such a disorder.